25-nA Modified Hybrid Ladder Converter with Efficient Output-Capacitor Charge Recycling and 90% Battery Lifetime Extension

Systems-on-Chip (SoCs) in wearable devices require a high-efficiency buck converter to convert battery voltage (VBAT, 2.8-4.2V for Li-ion battery) to Vo (supply voltage of SoC, < 1V). Integrating the buck converter with the SoC is cost-effective. Given that the fabrication process for SoC typically has $\text{low}-V_{\text{DS}}$ MOSFETs, stacking these MOSFETs as power switches in the buck converter to sustain up to 4.2V is a practical solution [1].